Multi-functional peripherals (MFPs) provide a plurality of functions, such as a printer function, a scanner function, etc., (sometimes referred to herein as an image forming apparatus). Multi-functional peripherals typically include a laser imaging device as the printer function. Efforts are continually being made to increase the printing/copying speed of such devices, while at the same time maintaining quality and reducing their cost.
Laser printers are designed to produce an image on paper or other print material by placing overlapping dots at virtual positions defined by a digital raster. A raster graphic image or bitmap is generally a rectangular grid of pixels, or points of color. These virtual positions in the raster are known as “pixels”, which is short for “picture elements”. In laser printers, the image is typically first produced on a charged photoconductive material by scanning the photoconductor with a laser beam in a sequence of scan lines. A laser scans the surface of the photoconductive material with a laser beam in the sequence of scan lines using a rotating polygonal mirror. As a line is scanned, or written, the laser beam is energized during the extent of each pixel that corresponds to a dot in the image. When the laser beam is energized, the portion of the photoconductor upon which the laser energy impinges is discharged, thereby producing a charge-pattern copy of the desired image on the photoconductor. The printed output is obtained by attracting toner to the charge-pattern and transferring the developed image to paper or other print material.
In order to increase the operating speed of such a laser imaging device, multiple laser beams can be used to concurrently scan multiple scan lines (i.e., line splitting) that are vertically offset from one another by an incremental amount. Such an imaging device is often referred to as a multiple-beam printer engine, or dual-beam laser printer engine (i.e., two laser beams). By concurrently scanning multiple laser beams, the time required to scan the photoconductive material is decreased, which results in an increased exposure and print speed. However, by using multiple-beam printer engines, an image plane buffer is required to drive each of the laser beams. It can be appreciated that typically only lower cost printers and/or multi-functional peripherals have a dual beam design, and the corresponding on board memory system for these lower cost printers and/or multi-functional peripherals is also limited.
In conventional implementations, the various printing operations are performed by a microprocessor under the control of firmware. Depending upon the type of print data (or image) entering the apparatus and the operations necessary to process the print data, a number of firmware routines are executed to complete the print data processing operations. As printers increase in density of dot placement (dots per inch), add gray scale capability (using a set of bits per pixel to define a gray scale level), and include color printing capability (requiring additional bits per pixel over monochrome printing), the time required for the image forming apparatus to process the print data increases. For example, in color printing the memory required to store the data used to print a page can reach thirty two times or more the memory required for a monochrome printer of the same resolution. To fully utilize the printing speed capabilities of the print engine, the apparatus must have the capability to process print data sufficiently fast to supply a continuous stream of print data to the print engine, thereby allowing the print engine to continuously print throughout the print job.
In a conventional image forming apparatus, microprocessors have the versatility to be programmed to perform the operations of the data delivered, the amount of memory associated with any given microprocessor generally directly increases the speed for performing these operations. In other words, the more available memory, the better potential performance throughput. However, typically, microprocessors with more memory are more costly than those with less memory.